Contracts Accounted for as Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	$ 306	$ 447	$ 505	$ 490	$ 560	$ 522
Net expected loss to be expensed (present value)	252
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	69
Contra-paid, net	24
Salvage and subrogation recoverable, net	410
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(251)
Net expected loss to be expensed (present value)	$ 252